EP240315a
GCN Circular 36055
Subject
X-ray transient EP240315a: second epoch e-MERLIN radio observations
Date
2024-04-09T16:22:07Z (2 years ago)
From
Lauren Rhodes at Oxford <lauren.rhodes@physics.ox.ac.uk>
Via
Web form
L. Rhodes (Oxford), G. Bruni (INAF-IAPS), L. Piro, G. Gianfagna, A.L. Thakur (INAF-IAPS), J. Bright, F. Carotenuto, S. Smartt, R. Fender (Oxford), P. Jonker (Radboud) report:
We observed the new Fast X-ray Transient EP240315a (Zhang et al., GCN 35931) with the e-Merlin radio telescope under the projects DD17003 (PI: Piro) and DD17004 (PI: Rhodes) at 5 GHz for a total of ~16 hours using a combination of two runs in two consecutive nights (from ~17:00 UT to ~01.00 UT, on March 27 and 28, 2024).
3C286 was used for flux scale calibration, and 0933-0819 for complex gain, respectively. The beam size was 0.15x0.03arcsec. Data was reduced with the eMERLIN pipeline and imaged with CASA. The image RMS was 21 uJy/beam.
We did not find statistically significant emission at a level above 5-sigma at the position of the optical counterpart (AT2024eju, Srivastav et al., GCN 35932). Thus, we estimated a 5 sigma upper limit of 105 uJy at 5 GHz. Our upper limit is consistent with the reports by Leung et al., GCN 35968 and Ricci et al., GCN 35990).
To search for fainter emission at the position of AT2024eju, we concatenated our two e-Merlin epochs (reported here and in Bruni et al., GCN 35980). Using a uniform weighting, we find a source with a flux density of about 70 uJy/beam at coordinates consistent with AT2024eju. The rms noise in this image is ~20uJy/beam.
We thank the e-Merlin staff for their excellent support.
GCN Circular 36008
Subject
Transient EP240315a: J-band observations of AT2024eju with WIRC
Date
2024-04-01T20:56:49Z (2 years ago)
From
nearley@caltech.edu
Via
Web form
Nicholas Earley (Caltech), Viraj Karambelkar (Caltech), Christoffer Fremling (Caltech), Mansi Kasliwal (Caltech):
We observed the location of the optical transient AT2024eju (Srivastav et al., GCN 35932) associated with the fast X-ray transient EP240315a (Zhang et al., GCN 35931; Chen et al. GCN 35951) in the near-infrared J-band with the Wide-Field Infrared Camera (WIRC, Wilson et al. 2003) on the 200-in Hale Telescope at Palomar Observatory.
Observations began at UTC 2024-03-20T04:27:45.313, roughly 4 days after detection in the X-ray. The observations consisted of a dithered set of 45 sec exposures for a total of ~30 minutes.
We detect a faint source at the location of AT2024eju with m_J ~ 22.5 mag (AB).
GCN Circular 35990
Subject
X-ray transient EP240315a: continued ATCA monitoring
Date
2024-03-29T11:07:44Z (2 years ago)
From
Roberto Ricci at INAF-IRA <ricci@ira.inaf.it>
Via
Web form
R. Ricci (INAF-IRA), D. Dobie (Swinburne/OzGrav), J. K. Leung (U. Toronto/HUJI), E. Troja (U. Rome)
We report on the results of a follow-up observation of the field of AT2024eju (Srivastav et al., GCN35932), the likely optical counterpart to the fast X-ray transient EP240315a (Zhang et al., GCN35931), with the Australia Telescope Compact Array (ATCA) under project code CX564. The observations were taken from 2024-03-26 06:20 UT to 2024-03-26 11:24 UT, in a single run, at 5.5 and 9 GHz. The primary calibrator was 1934-638 and the phase calibrator 0941-080.
From a preliminary analysis, the radio source reported in our previous GCN (Leung et al., GCN 35968) continues to be detected at a comparable flux level, ~0.1 mJy. Monitoring with ATCA will continue to assess the variability of the source.
We thank the CSIRO Space and Astronomy staff, in particular Jamie Stevens, for supporting these observations in a timely manner. We acknowledge the Gomeroi people as the traditional owners of the Observatory site. The Australia Telescope Compact Array is part of the Australia Telescope National Facility (https://ror.org/05qajvd42) which is funded by the Australian Government for operation as a National Facility managed by CSIRO.
GCN Circular 35982
Subject
X-ray transient EP 240315a: Second epoch Chandra observations
Date
2024-03-27T09:06:39Z (2 years ago)
From
Andrew Levan at Radboud University <a.levan@astro.ru.nl>
Via
Web form
A.J. Levan (Radboud & Warwick), P.G. Jonker (Radboud), D.B. Malesani (DAWN/NBI & Radboud), N.R. Tanvir (Leicester), B.P. Gompertz (Birmingham), A. Saccardi (GEPI/Obs. de Paris), A. de Ugarte Postigo (CNRS/OCA & LAM), A. Martin-Carrillo (UCD), D. Perley (LJMU), D. Xu (NAOC), G. Tagliaferri (INAF, Brera), J. Palmerio (GEPI/Obs. de Paris)), K.E. Heintz (DAWN/NBI), K. Wiersema (Hertfordshire), M. Grazia Bernardini (INAF, Brera), M. Ferro (INAF, Brera), P. Jakobbson (U. Iceland), P. D’Avanzo (INAF, Brera), R. Salvaterra (INAF, Milan), S. Vergani (GEPI/Obs. de Paris), G. Pugliese (API, Amsterdam), Y. Julakanti (Leicester) report for the Stargate collaboration:
We obtained a second epoch of Chandra observations of EP240315a (Zhang et al., GCN 35931; Chen et al., GCN 35951) beginning at 04:34 on 26 March 2024, approximately 10.4 days after the transient detection and 6 days from the first epoch of observations (Levan et al., GCN 35963). A total of 18.5 ks of observations were obtained (compared to 10 ks at the first epoch). At the location of AT2024eju (Srivastav et al. GCN 35932) we do not detect any source. More formally, we identify a single photon at the source location, and set a 2-sigma upper limit of <2.4e-4 count s^-1 at this epoch.
The inferred decay rate from 3 days to 10.4 days is steeper than t^-2.1, and suggests a relatively rapid decay. This is consistent with the post-jet break decay rate for a GRB afterglow.
We again thank Pat Slane, Vinay Kashyap and the staff of the CXC for their excellent support and rapid scheduling of these observations.
GCN Circular 35980
Subject
X-ray transient EP240315a: e-MERLIN radio observations
Date
2024-03-26T14:45:28Z (2 years ago)
From
Gabriele Bruni at INAF <gabriele.bruni@inaf.it>
Via
Web form
G. Bruni (INAF-IAPS), L. Rhodes (Oxford), L. Piro, G. Gianfagna, A.L. Thakur (INAF-IAPS), J. Bright, F. Carotenuto, S. Smartt, R. Fender (Oxford), P. Jonker (Radboud) report:
We observed the new Fast X-ray Transient EP240315a (Zhang et al., GCN 35931) with the e-Merlin radio telescope under the projects DD17003 (PI: Piro) and DD17004 (PI: Rhodes) at 5 GHz for a total of ~16 hours using a combination of two runs in two consecutive nights (from ~17:30 UT to ~02.00 UT, on March 20 and 21, 2024).
3C286 was used for flux scale calibration, and 0933-0819 for complex gain, respectively. The beam size was 275x104 milli-arcsec. Data was reduced with the e-MERLIN pipeline and imaged with CASA. The image RMS was 15 uJy/beam.
We did not find statistically significant emission at a level above 5-sigma at the position of the optical counterpart (AT2024eju, Srivastav et al., GCN 35932). Thus, we estimated a 5-sigma upper limit of 75 uJy at 5 GHz. Scintillation could be a possible explanation for the large variability with respect to the previous radio detection at the same frequency (Leung et al., GCN 35968).
Further e-Merlin observations are planned. We thank the e-Merlin staff for their excellent support.
GCN Circular 35979
Subject
X-ray transient EP240315a: Ondrejov D50 optical limit
Date
2024-03-26T11:07:49Z (2 years ago)
From
Martin Jelinek at Astro.Inst-AVCR,Ondrejov <martin.jelinek@asu.cas.cz>
Via
legacy email
Alzbeta Malenakova, Jan Strobl, Martin Jelinek, Rene Hudec and Cyril Polasek
(ASU CAS Ondrejov, CZ), report:
We observed the field of the fast X-ray transient EP240315a detected by Einstein Probe (Zhang et al., GCN 35931) and its optical counterpart AT2024eju detected by ATLAS (Srivastav et al., GCN 35932) with the 50 cm robotic telescope (D50) of Ondrejov observatory in Czech Republic. We obtained a set of 120s SDSS-r' exposures starting at 23:03 UT on March 16.
We measure the optical limit r' > 21.1 in a combined 26x120s image with a mean time T-T0 27.43h post detection, which is in agreement with other observations at similar epoch (e.g. Chen et al., GCN 35938, Leonini et al., 35944).
GCN Circular 35968
Subject
X-ray transient EP240315a: ATCA detection of radio counterpart
Date
2024-03-20T22:45:33Z (2 years ago)
From
James Leung at U. Toronto / HUJI <jamesk.leung@utoronto.ca>
Via
Web form
J. K. Leung (U. Toronto/HUJI), R. Ricci (INAF-IRA), D. Dobie (Swinburne/OzGrav), E. Troja (U. Rome)
We observed the field of AT2024eju (Srivastav et al., GCN35932), the likely optical counterpart to the fast X-ray transient EP240315a (Zhang et al., GCN35931), with the Australia Telescope Compact Array (ATCA) under project code CX564. The observations were taken on two consecutive days, from 2024-03-19 06:30 UT to 2024-03-19 09:00 UT and from 2024-03-20 06:30 UT to 2024-03-20 09:30 UT, both at 5.5 and 9 GHz.
In our preliminary analysis, we detect a radio source at both 5.5 and 9 GHz, with a flux density of ~0.1mJy. The position of the source is consistent with that of EP240315a (Zhang et al., GCN35931), AT2024eju (Srivastav et al., GCN35932), and the radio counterpart detected at 3 GHz by MeerKAT (Carotenuto et al., GCN35961).
Further ATCA observations are planned.
We thank the CSIRO Space and Astronomy staff, in particular Jamie Stevens, for supporting these observations in a timely manner. We acknowledge the Gomeroi people as the traditional owners of the Observatory site. The Australia Telescope Compact Array is part of the Australia Telescope National Facility (https://ror.org/05qajvd42) which is funded by the Australian Government for operation as a National Facility managed by CSIRO.
GCN Circular 35963
Subject
X-ray transient EP 240315a: Chandra observations
Date
2024-03-19T11:31:23Z (2 years ago)
From
Andrew Levan at Radboud University <a.levan@astro.ru.nl>
Via
Web form
A.J. Levan (Radboud & Warwick), P.G. Jonker (Radboud), D.B. Malesani (DAWN/NBI & Radboud), N.R. Tanvir (Leicester), B.P. Gompertz (Birmingham), A. Saccardi (GEPI/Obs. de Paris), A. de Ugarte Postigo (CNRS/OCA & LAM), A. Martin-Carrillo (UCD), D. Perley (LJMU), D. Xu (NAOC), G. Tagliaferri (INAF, Brera), J. Palmerio (GEPI/Obs. de Paris)), K.E. Heintz (DAWN/NBI), K. Wiersema (Hertfordshire), M. Grazia Bernardini (INAF, Brera), M. Ferro (INAF, Brera), P. Jakobbson (U. Iceland), P. D’Avanzo (INAF, Brera), R. Salvaterra (INAF, Milan), S. Vergani (GEPI/Obs. de Paris), G. Pugliese (API, Amsterdam), Y. Julakanti (Leicester) report for the Stargate collaboration:
We obtained observations of EP240315a (Zhang et al., GCN 35931) with the Chandra X-ray observatory. Observations began at 20:13 on 18 March 2024, 72 hours after the flare detection. The source was placed at the default aim point on the S3 chip for a total exposure time of 10 ks. At the location of AT2024eju (Srivastav et al., GCN 35932) we clearly detect an X-ray counterpart with a source flux of (3.3+/- 0.5)e-3 cps.
For the same spectral parameters inferred from the EP follow-up telescope observations, and at z = 4.859 (Saccardi et al., GCN 35936; Quirola-Vásquez et al., GCN 35960) the source has an X-ray luminosity of L_X ~ 2e46 erg/s . The decay from the EP follow-up telescope observations at t+42 hours (Chen et al. GCN 35951) to the Chandra exposure at t+72 hours post burst is ~t^-1.6. Both of these are typical of the properties seen in long GRBs, although the luminosity is towards the higher end.
We thank Pat Slane, Vinay Kashyap and the staff of the CXC for their excellent support and rapid scheduling of these observations.
GCN Circular 35962
Subject
X-ray transient EP240315a: GTC/HiPERCAM photometry
Date
2024-03-18T22:39:47Z (2 years ago)
From
P.G. Jonker at Radboud University <p.jonker@astro.ru.nl>
Via
Web form
P. G. Jonker (Radboud Univ.), S. Littlefair (Sheffield Uni.), F. E. Bauer (PUC), A. J. Levan (Radboud Univ. & Warwick Univ.), D. B. Malesani (DAWN/NBI and Radboud Univ.), Maria E. Ravasio (Radboud Univ.), M.A.P. Torres (IAC), V. Dhillon (Sheffield Uni.), D. García Álvarez (GTC), A. M. García (GTC), on behalf of a larger collaboration:
We observed the optical counterpart AT2024eju (Srivastav et al., GCN 35932) of the fast X-ray transient EP240315a reported by the Einstein Probe WXT instrument (Zhang et al., GCN 35931), using the GTC/HiPERCAM imager. We obtained 80 exposures of 30 seconds each in u’g’r’i’z’ simultaneously. The observations started at 21:10 UT on Mar 17, 2024. We clearly detected the source in the r’, i’, and z’ bands.
The z’-band magnitude was 22 (AB mag).
We acknowledge the excellent support from the GTC staff.
GCN Circular 35961
Subject
X-ray transient EP240315a: MeerKAT radio detection
Date
2024-03-18T21:47:26Z (2 years ago)
From
Francesco Carotenuto at University of Oxford <francesco.carotenuto@physics.ox.ac.uk>
Via
Web form
F. Carotenuto, J. Bright (Oxford), P. G. Jonker (Radboud), R. Fender, L. Rhodes (Oxford) report on behalf of a larger collaboration:
We observed the new Fast X-ray Transient EP240315a (Zhang et al., GCN 35931) with the MeerKAT radio telescope at 3.0 GHz for a total of 1 hour starting on 18 March 2024 at 16:53 UTC. J1939-6342 and 3C237 were used as flux and complex gain calibrators, respectively. Using the South African Radio Astronomy Observatory Science Data Pipeline image, we find an unresolved source at the position of the optical counterpart of the FXT AT2024eju (Srivastav et al., GCN 35932) with a flux density of ~30uJy/beam. The rms noise in the field is 8.5 uJy/beam. Further MeerKAT observations are planned.
We thank the staff at the South African Radio Astronomy Observatory for the rapid scheduling of these observations.
GCN Circular 35960
Subject
X-ray transient EP240315a: GTC/OSIRIS spectroscopic redshift confirmation
Date
2024-03-18T21:46:12Z (2 years ago)
From
P.G. Jonker at Radboud University <p.jonker@astro.ru.nl>
Via
Web form
J. Quirola-Vásquez (Radboud Univ.), P.G. Jonker (Radboud Univ.), A. J. Levan (Radboud Univ. & Warwick Univ.), F. E. Bauer (PUC), D. B. Malesani (DAWN/NBI and Radboud Univ.), Maria E. Ravasio (Radboud Univ.), M.A.P. Torres (IAC), A. M. García (GTC) on behalf of a larger collaboration:
We observed the optical counterpart AT2024eju (Srivastav et al., GCN 35932) of the fast X-ray transient EP240315a reported by the Einstein Probe WXT instrument (Zhang et al., GCN 35931) and followed-up by its FXT instrument (Chen et al., GCN 35951), using the GTC/OSIRIS spectrograph. Our spectra cover the wavelength range 5100-10000 AA and consist of 3 exposures of 1200 seconds each. Observations started at 22:54:51 UT on Mar 16, 2024 (~27 hr after the X-ray trigger). We detect a faint trace, with the Lyman break and several absorption features which we identify as due to OIλ1302.17, SiIIλ1304.37, and SiIVλλ1393.76/1402.77. Therefore, we confirm the redshift identification of z = 4.859 determined by Saccardi et al. (GCN 35936) using VLT/X-shooter.
We acknowledge the excellent support from the GTC staff.
GCN Circular 35956
Subject
X-ray transient EP240315a: PRIME near infrared detection
Date
2024-03-18T18:35:29Z (2 years ago)
From
Joe Durbak at UMD <gcn.joedurbak@gmail.com>
Via
Web form
O. Guiffreda (UMD), J. Durbak (UMD), A. S. Kutyrev (NASA/GSFC), E. Troja (U Rome), K. De (MIT), S. B. Cenko (NASA/GSFC)
Following the Einstein Probe detection (GCN 35931) of EP240315a, we observed the transient field in the J filter with PRIME ~1 day after the Einstein Probe detection.
At the position of the optical transient AT2024eju reported by ATLAS (Srivastav et al. GCN 35932), we detect an uncatalogued source in J band. Using nearby VISTA Hemispherical Survey (VHS) stars for preliminary calibration we derive the following magnitude, not corrected for Galactic extinction:
Filter | Mag(VISTA) | SNR | Seeing | Total exposure time (s) | UT Date-time at start
-------|----------------|-----|--------|------------------------------------------------
J | 19.7 +/- 0.3 | 6.0 | 1.3” | 675 | 2024-03-16T19:14:20
This result is consistent with GROND detection (Rau GCN 35937). Conditions were intermittently cloudy, resulting in higher than usual photometric error.
PRIME is a 1.8m telescope with 1.56 square degree FOV (0.5 arcsec/pixel) located in Sutherland, South Africa.
Further observations are planned.
We thank the Osaka University observers at PRIME and the staff at SAAO for their support with these observations.
GCN Circular 35954
Subject
X-ray transient EP240315a: 3.6 m TNG NIR detection
Date
2024-03-18T15:24:39Z (2 years ago)
From
Youdong HU at INAF-OAB <huyoudong072@hotmail.com>
Via
Web form
Y.-D. Hu, P. D'Avanzo, M. Ferro, R. Brivio, S. Covino, D. Fugazza, S. Campana (INAF-OAB), A. Rossi (INAF-OAS), D. B. Malesani (DAWN/NBI & Radboud Univ.), A. Melandri (INAF-OAR), L. Di Fabrizio, C. Padilla (INAF-TNG) on behalf of the CIBO collaboration report:
We observed the field of the fast X-ray transient EP240315a detected by the Einstein Probe mission (Zhang et al., GCNC 35931; Chen et al. GCNC 35951) with the Italian 3.6m TNG telescope equipped with the near-infrared camera NICS to follow up its optical counterpart AT2024eju (TNS Astronomical Transient Report No. 205383). A series of images were obtained with the H filter starting on 2024-03-17 19:58:11 UT (i.e. 2.02 days post T0). The optical counterpart (Srivastav et al., GCN 35932, 35933; Jiang et al., GCN 35935; Saccardi et al., GCN 35936; Rau GCN 35937; Chen GCN 35938; Lipunov, GCN 35940; Leonini et al., GCN 35944; Pankov et al., GCN 35945, Pankov et al. GCNC 35952) is clearly detected in the co-added image with a preliminary result of H(Vega)~19.8 mag (calibrated against the 2MASS catalogue).
GCN Circular 35952
Subject
X-ray transient EP240315a/AT2024eju: TShAO (Zeiss-1000) observatory optical upper limit
Date
2024-03-18T14:52:47Z (2 years ago)
From
Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>
Via
legacy email
N. Pankov (HSE, IKI), I. Reva (FAI), A. Pozanenko (IKI), S. Belkin (IKI), A. Volnova (IKI) report on behalf of IKI GRB FuN:
We observed the field of the X-ray transient EP240315a (Zhang et al., GCN 35931) till now also detected by Follow-up X-ray Telescope of Einstein Probe (Chen et al., GCN 35951). The optical counterpart AT2024eju discovered by ATLAS (Srivastav et al., GCN 35932, 35933) and observed in optic (Jiang et al., GCN 35935; Saccardi et al., GCN 35936; Rau GCN 35937; Chen GCN 35938; Leonini et al., GCN 35944; Pankov et al., GCN 35945) was observed with Zeiss-1000 telescope of Tien Shan Astronomical Observatory stating on 2024-03-17 (UT) 14:12:06 in R filter. We do not detect the optical counterpart. Preliminary photometry of the filed is following
Date UT start t-T0 Filter Exp. OT Err. UL(3sigma)
(mid, days) (s)
2024-03-17 14:12:06 1.77526 R 35*120 n/d n/d 22.3
The photometry is based on nearby USNO-B1.0 (R2) stars.
GCN Circular 35951
Subject
X-ray transient EP240315a: EP-FXT detection of the X-ray afterglow
Date
2024-03-18T13:38:26Z (2 years ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
legacy email
Y. Chen, S.M. Jia, W.W. Cui, C.K. Li, D.W. Han, J. Wang, W. Li, X.F. Zhao, J.J. Xu, H.S. Zhao, J. Guan, J. Zhang, L.M. Song, F.J. Lu, C.Z. Liu, S.N. Zhang (IHEP, CAS), W.J. Zhang, X. Mao, W.D. Zhang, D.Y. Li, T.Y. Lian, Y. Liu, W. Yuan (NAOC, CAS), K. Nandra, A. Rau, P. Friedrich, N. Meidinger, V. Burwitz (MPE), E. Kuulkers, Andrea Santovincenzo (ESA), P. O'Brien (UoL) and B. Cordier (CEA) on behalf of the Einstein Probe team
Following the detection of the fast X-ray transient EP240315a (Zhang et al., GCN 35931) and its optical counterpart (Srivastav et al., GCN 35932, 35933; Jiang et al., GCN 35935; Saccardi et al., GCN 35936; Rau GCN 35937; Chen GCN 35938; Lipunov, GCN 35940; Leonini et al., GCN 35944; Pankov et al., GCN 35945), we performed observations of EP240315a with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe mission. The observations began at 2024-03-17T14:10:00, about 42 hours after the EP-WXT detection. The exposure time is 3758 seconds. An X-ray afterglow was detected at R.A. = 141.6483 deg, DEC = -9.5335 deg, with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic), 3.2 arcsec away from the position of the optical counterpart AT2024eju (Srivastav et al., GCN 35932). The spectrum can be fitted with an absorbed power-law model with NH fixed at the Galactic value of 4.2E20 cm-2 and a photon index of 1.4(-0.5, +0.5). The derived flux in 0.3-10 keV is 1.8(-0.7, +1.4)E-13 erg/s/cm2 (90% C.L.). There is no cataloged X-ray source within the error circle, consistent with this source being the afterglow of EP240315a. Daily monitoring of the source with FXT is planned over the next few days.
Please note that EP-FXT is currently undergoing in-flight calibration. The derived source parameters may be subject to larger uncertainties, so please use them with caution. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). EP is a mission of the Chinese Academy of Sciences in collaboration with ESA, MPE and CNES.
GCN Circular 35945
Subject
X-ray transient EP240315a: Kitab observatory optical upper limitns
Date
2024-03-17T16:17:06Z (2 years ago)
From
Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>
Via
legacy email
N. Pankov (HSE, IKI), A. Schmalz (KIAM), A. Pozanenko (IKI), S. Belkin (IKI), A. Volnova (IKI), A. Novichonok (Petrozavodsk State University, KIAM) report on behalf of IKI GRB FuN:
We observed the field of the optical counterpart of the X-ray transient EP240315a (Einstein Probe, GCN 35931, Zhang et al.; GCN 35932, GCN 35933, Srivastav et al.; GCN 35935, Jiang et al.; GCN 35937, Rau; GCN 35938, Chen et al.; GCN 35944, Leonini et al.) with Kitab-ISON RC-36 telescope starting on 2024-03-16 (UT) 18:00:00 in Clear filter. We do not detect the optical afterglow (Srivastav et al., GCN 35932) at redshift of z = 4.859 (Saccardi et al., GCN 35936). Preliminary photometry of the filed is following
Date UT start t-T0 Filter Exp. OT Err. UL(3sigma)
(mid, days) (s)
2024-03-16 18:00:00 0.91685 Clear 22*60 n/d n/d 19.2
The photometry is based on the nearby USNO-B1.0 (R2) stars.
GCN Circular 35944
Subject
X-ray transient EP240315a: Montarrenti Observatory optical upper limit
Date
2024-03-17T14:48:52Z (2 years ago)
From
Simone Leonini at Montarrenti Observatory (Siena, Italy) <s.leonini@iol.it>
Via
Web form
S. Leonini, M. Conti, P. Rosi, L.M. Tinjaca Ramirez (Montarrenti Observatory, Siena, Italy, part of UAI/SSV-GRB section), M.G. Dainotti (National Astronomical Observatory of Japan), Y. Niino (Tokyo University, Institute of Astronomy), K. Kalinowski (Aarhus University, Department of Physics and Astronomy) and B. De Simone (Universita' degli Studi Di Salerno) report:
We observed the field of the possible optical countepart of the X-ray transient EP240315a (Einstein Probe, GCN 35931, Zhang et al.; GCN 35932, GCN 35933, Srivastav et al.; GCN 35935, Jiang et al.; GCN 35937, Rau; GCN 35938, Chen et al.) with the automated and remoted 0.53m Ritchey-Chretien telescope at Montarrenti Observatory (Siena, Italy, IAU code C88).
The observations were started at 2024-03-16 20:10:21 UT (approximately 24 hours after the discovery of the X-ray transient) stacking 32x40s V and Rc-band CCD images.
We have not found any optical transient candidate within the error-box of the EP mission position with the following upper limit:
MJD Filter Limit SNR
60385.8572 V > 20.43 6.9
60385.8578 Rc > 20.90 5.4
Magnitude was calibrated with the nearby PanSTAR stars converted using Lupton (2005) equations. No correction for galactic dust extinction was applied.
GCN Circular 35940
Subject
X-ray transient EP240315a: orphan FXT?
Date
2024-03-17T10:04:11Z (2 years ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
legacy email
V.Lipunov (Lomonosov MSU, Perevoschikov Moscow Observatory)
The recently launched space mission of the Chinese Academy of Sciences in collaboration with ESA, MPE and CNES Einstein Probe mission (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics) reported the discovery of the fast soft X-ray transient (FXT) EP240315a (Zhagn et al., GCN 35931).
Publication is about an event lasting ~1600 seconds. The spectrum of the ATLAS optical counterpart AT2024eju (Srivastav et al., GCN 35932) unambiguously establishes the cosmological nature of EP240315a with redshift z = 4.859 and a possible connection with Gamma Ray Bursts (Saccardi et al., GCN 35936).
Note that the phenomenon of fast X-ray flares was actually predicted within the framework of the Spinar paradigm (Lipunov & Gorbovskoy, 2007, ApJ, v.665, L97; Lipunov & Gorbovskoy, 2008, MNRAS, v.383, 1397.; Lipunova et al., 2009, MNRAS, v.397,1695).
In the case of core collapse, which has an increased spin monentum and a weak magnetic field, the phenomenon of fast X-ray bursts can occur without the phenomenon of a gamma-ray burst at all. The corresponding diagram is available at http://observ.pereplet.ru/images/spinar_dogma.jpg)
GCN Circular 35938
Subject
X-ray transient EP240315a: Kinder follow-up observations for AT 2024eju with Lulin observatory
Date
2024-03-17T08:26:16Z (2 years ago)
From
Janet Chen at National Central University <janetstars@gmail.com>
Via
Web form
T.-W. Chen (NCUIA), S. Yang (HNAS), M.-H. Lee, H.-Y. Hsiao, C.-H. Lai, A. Sankar.K, C.-C. Ngeow, Y.-C. Pan, C.-S. Lin, W.-J. Hou, H.-C. Lin, J.-K. Guo (all NCUIA), S. Srivastav, S. Smartt (both Oxford) and M. Fulton, T. Moore, C. Angus, A. Aamer (all QUB) report:
We observed the field of AT 2024eju (Srivastav et al., GCN 35932), a possible optical counterpart for the EP240315a (Zhang et al., GCN 35931) found by ATLAS, using the 40cm SLT at Lulin Observatory, Taiwan as part of the Kinder collaboration (Chen et al., AstroNote 2021-92).
The first SLT epoch of observations started at 16:09 UT on 16 of March 2024 (MJD = 60385.673), 0.83 days after the discovery of the X-ray transient. The r-band images were combined from 6 frames, each with a 300-second exposure time, taken under seeing conditions averaging 2.0" and at a median airmass of 1.61.
We used the Kinder pipeline (Yang et al. A&A 646, A22) to measure the PSF photometry on the source location, after subtracted with the Pan-STARRS1 template image. We obtained the following preliminary upper limit (in the AB system):
r > 21.5 mag (SNR = 2.2 sigma).
The given limit is derived based on calibrating against Pan-STARRS1 field stars and is not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V) = 0.04 mag in the direction of the burst (Schlafly & Finkbeiner 2011).
Our r-band limit is deeper than the LT follow-up observations on MJD 60385.848 (Srivastav et al., GCN 35933) and the Nanshan/HMT limit on MJD 60385.69 (Jiang et al., GCN 35935). By direct comparison with the ATLAS o band detection of AT 2024eju, we deduce that the source experienced a rapid fade of more than 1.86 magnitudes within a span of 0.78 days.
Despite the SNR of the measurement being only 2.2 sigma, which falls below our threshold, we were still able to see a slightly faint source in the subtracted image by eye at the position of AT 2024eju. We thus chose to measure the faint source using a lower threshold and obtained an r-band magnitude of 21.45 +/- 0.22.
GCN Circular 35937
Subject
X-ray transient EP240315a: GROND J-band detection
Date
2024-03-17T07:54:44Z (2 years ago)
From
Arne Rau at MPE <arau@mpe.mpg.de>
Via
Web form
Arne Rau (MPE):
The location of the optical transient AT2024eju (Srivastav et al., GCN35932), discovered within the error circle of the fast X-ray transient EP240315a reported by Einstein Probe n (Zhang et al., GCN 35931), was observed with the optical/NIR imager GROND (Greiner et al. 2008) at the MPG 2.2m telescope at the ESO La Silla Observatory on 2024 March 17th 02:50:23 UT (MJD 60386.118).
With an exposure of 1200s, the source is detected in the J-band at m_vega=19.6+/-0.2 (m_AB=20.5+/-0.2).
We thank the 2.2m staff member, Paul Eigenthaler, for the rapid execution of the observation.
GCN Circular 35936
Subject
X-ray transient EP240315a: VLT/X-shooter spectroscopic redshift of z = 4.859
Date
2024-03-17T06:54:26Z (2 years ago)
From
Andrea Saccardi at Observatoire de Paris <andrea.saccardi@obspm.fr>
Via
Web form
A. Saccardi (GEPI/Obs. de Paris), A. J. Levan (Radboud Univ. & Warwick Univ.), Z. Zhu (NAOC), B. P. Gompertz (U. Birmingham), S. D. Vergani (GEPI/Obs. de Paris & IAP & INAF/OABr), G. Pugliese (API), D. Xu (NAOC), D. B. Malesani (DAWN/NBI and Radboud Univ.), report on behalf of the Stargate collaboration:
We observed the field of the ATLAS optical counterpart AT2024eju (Srivastav et al., GCN 35932) of the fast X-ray transient EP240315a reported by the WXT instrument during the commissioning phase of the Einstein Probe mission (Zhang et al, GCN 35931) using the ESO/VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Our spectra cover the wavelength range 3000-21000 AA, and consist of 4 exposures of 1200 s each. Observations started at 01:02:52 UT on Mar 17 2024 (~29 hr after the trigger). We detect a clear continuum across both VIS and NIR arms. From the detection of a Lya absorption at ~7120 AA and multiple absorption features, which we interpret as being due to OI, SiII, NV, CIV and SiIV, we infer a redshift of z = 4.859. We also note the presence of additional absorption features likely due to multiple intervening systems. The high redshift of the transient suggests a highly energetic event and potentially links this Fast X-ray Transient to a GRB-like phenomena.
We acknowledge the excellent support from the ESO staff in Paranal, in particular Joe Anderson and Matias Jones.
GCN Circular 35935
Subject
X-ray transient EP240315a: Nanshan/HMT optical upper limit
Date
2024-03-17T06:52:41Z (2 years ago)
From
Dong Xu at NAOC/CAS <dxu@nao.cas.cn>
Via
Web form
S.Q. Jiang, Z.P. Zhu, X. Liu, J. An, S.Y. Fu, T.H. Lu, D. Xu (NAOC), X. Gao (Urumqi No.1 Senior High School), J.Z. Liu (XAO) report on behalf of a large collaboration:
We observed the field of EP240315a detected by Einstein Probe (EP, Zhang et al., GCN 35931) using the HMT-0.5m telescope located at Nanshan, Xinjiang, China. We obtained 30 x 90 s frames without any filter.
No uncatalogued optical transient is detected within or near the EP/WXT error circle, down to a limiting magnitude of r ~ 20.9 at a median time of 20.44 hr post-trigger, calibrated with the nearby PanSTAR field.
The previously reported ATLAS optical counterpart candidate, AT2024eju, (Srivastav et al., GCN 35932) is not present in the HMT co-added image, indicating that it has decayed significantly. Our non-detection is consistent with that from LT (Srivastav et al., GCN 35933).
GCN Circular 35932
Subject
X-ray transient EP240315a: ATLAS detection of a possible optical counterpart AT2024eju
Date
2024-03-16T22:08:06Z (2 years ago)
From
S. Srivastav at Oxford <shubhamsrivastav@gmail.com>
Via
Web form
S. Srivastav, S. J. Smartt (Oxford), M. D. Fulton, K. W. Smith, A. Aamer, C. R. Angus, M. McCollum, T. Moore, M. Nicholl, X. Sheng, J. Weston, D. R. Young (QUB), P. Ramsden (QUB/Birmingham), L. Shingles (GSI/QUB), A. Andersson, J. H. Gillanders, L. Rhodes, H. Stevance (Oxford), J. Sommer (LMU/QUB), L. Denneau, J. Tonry, H. Weiland, A. Lawrence, R. Siverd (IfA, University of Hawaii), N. Erasmus, W. Koorts (South African Astronomical Observatory), A. Jordan, V. Suc (UAI, Obstech), A. Rest (STScI), T.-W. Chen (NCU), C. Stubbs (Harvard):
Here we report the ATLAS detection of an optical transient AT2024eju, discovered within the error circle of the fast X-ray transient EP240315a reported by the Einstein Probe mission (Zhang et al, GCN 35931).
ATLAS is a quadruple 0.5-m telescope system with two units in Hawaii, one in Chile and one in South Africa (see Tonry et al. 2018, PASP, 130:064505), routinely surveying the visible sky on a daily basis. We promptly process all data with our transient science server (Smith et al. 2020, PASP, 132:085002).
ATLAS detected AT2024eju (TNS Astronomical Transient Report No. 205383) during normal survey mode observations at an AB magnitude of 19.37 +/- 0.14 in the ATLAS-cyan band on MJD 60384.887, around 1.1 hrs following the detection of the X-ray transient. The position of AT2024eju is 0.8 arcmin offset from the coordinates reported by Zhang et al. We found no historical detections of any excess optical flux in ATLAS at this position through forced photometry.
Spectroscopic classification of this transient is encouraged.
GCN Circular 35931
Subject
Einstein Probe detected of a fast X-ray transient EP240315a
Date
2024-03-16T15:49:37Z (2 years ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
legacy email
W. J. Zhang (NAOC, CAS), X. Mao (NAOC, CAS), W. D. Zhang (NAOC, CAS), H. Y. Liu (NAOC, CAS), Y. Liu (NAOC, CAS), C. Zhang (NAOC, CAS),
Z. X. Ling (NAOC, CAS), C. C. Jin (NAOC, CAS), H. Q. Cheng (NAOC, CAS), W. Chen (NAOC, CAS), C. Z. Cui (NAOC, CAS), D. W. Fan (NAOC, CAS),
H. B. Hu (NAOC, CAS), J. W. Hu (NAOC, CAS), M. H. Huang (NAOC, CAS), D. Y. Li (NAOC, CAS), T. Y. Lian (NAOC, CAS), M. J. Liu (NAOC, CAS),
Z. Z. Lv (NAOC, CAS), H. W. Pan (NAOC, CAS), X. Pan (NAOC, CAS), H. Sun (NAOC, CAS), W. X. Wang (NAOC, CAS),Y. L. Wang (NAOC, CAS),
Q. Y. Wu (NAOC, CAS), X. P. Xu (NAOC, CAS), Y. F. Xu (NAOC, CAS), H. N. Yang (NAOC, CAS), M. Zhang (NAOC, CAS), S. N. Zhang (IHEP, CAS),
Z. Zhang (NAOC, CAS), D. H. Zhao (NAOC, CAS), E. Kuulkers (ESA), P. O'Brien (Univ. of Leicester) and W. Yuan (NAOC, CAS), on behalf of the Einstein Probe team
We report on the detection of a fast X-ray transient EP240315a at 2024-03-15T20:10:44 (UTC) by the Wide-field X-ray Telescope (WXT) on board
the Einstein Probe (EP) mission during a calibration observation. The position of the source is R.A. = 141.644 deg, DEC = -9.547 deg (J2000)
with an uncertainty of 3 arcmin (radius, 90% C.L. statistical and systematic). The light curve of the source shows a multi-peak profile.
The transient event lasts for ~1600 seconds and has a peak flux of ~3e-9 erg/s/cm^2 in the 0.5-4 keV band. The averaged spectrum can be fitted
by an absorbed power-law with NH = 1.5(-0.9/+1.0) x 10^21 cm^-2 and a photon index of 1.7(-0.4/+0.4). The derived average unabsorbed 0.5 - 4.0 keV
flux is 5.3(-0.7/+1.0) x 10^-10 erg/s/cm^2. However, we note that the derived source parameters may be subject to larger uncertainties than those
quoted here since in-orbit calibration of the instrument is still in progress.
No previously known bright X-ray sources have been found within the 3 arcmin region around the source position, with only one optical counterpart
of white dwarf candidate located at the distance of ~380 pc. Based on the shape and timescale of the observed flare light curve, we tend to consider
that the source is not a stellar flare, although this cannot be ruled out. A Swift target of opportunity observation has been proposed, and further
follow-up observations are strongly encouraged to identify the nature of this X-ray flare.
The above observation was made with the WXT instrument during the commissioning phase of EP. Launched on January 9, 2024, EP is a space X-ray observatory
to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). EP is a mission of the Chinese
Academy of Sciences in collaboration with ESA, MPE and CNES.